An estimated 40% of illegal immigrants in this country weren’t smuggled across the border. They came here on legal visas and simply stayed after their visa expired. While the implementation of a system to track when visa-holders exit is one of the “triggers” in the Gang of 8 enforcement provisions, on Tuesday the Senate Judiciary Committee rejected the inclusion of a secure, high-tech system to monitor exits of visa holders. With the vote, four of Sen. Marco Rubio’s fellow “Gang” members rejected a provision he supports.

Currently, the US monitors when visa-holdes enter the country. It does nothing to monitor, or even verify, when they leave. For more than two decades, in the aftermath of the 9-11 attacks, Congress has pushed the Immigration Service to establish a system to monitor whether visa-holder exit the country when their visa expires. Current law requires DHS to establish a system using bio-metrics like fingerprints and retina scans. The intent is for the federal government to know immediately whether a visitor has overstayed their visa.

DHS Director of Counterterrorism, Jay Cohen testified in March, 2012 before the House that that “DHS intends to propose a plan for a biometric exit system that could flag visa overstays… and would enable DHS personnel to use fingerprints and photographs to identify offenders for investigation and removal from the United States.” The plan was never developed.

In the current Senate amnesty legislation, the biometric system would be scrapped and replaced with a “biographic” system that would just check names, date-of-birth, etc. It is much weaker than current law and has greater potential for fraud.

Tuesday morning, the Senate Judiciary considered an amendment from Sen. Jeff Sessions that would have reinstated the biometric system mandate. Sen. Marco Rubio supported the amendment. His two fellow GOP “Gang” negotiators, however, Sens. Graham and Flake, joined Senate Democrats on the committee to reject the amendment.

“Immigration reform must include the best exit system possible because persons who overstay their authorized stay are a big reason we now have so many illegal immigrants,” Alex Conant, a spokesman for Rubio, told The Hill. “We wanted the Judiciary Committee to strengthen the legislation by adding biometrics to the new exit system, and we were disappointed by this morning’s vote.”

The “Gang” negotiators have been extraordinarily unified in rejecting efforts to amend their legislation. Sen. Rubio has assured conservatives worried about border security that the negotiators would consider changes to strengthen the legislation. That hasn’t happened in committee and it is unlikely to happen on the floor of the Senate.

Supporters of increased enforcement will have to wait for House action to have any real chance of success.